Make sure to rename this program to stoplight
or something similar so that you don’t confuse it with the player program!
Red Light Green Light
This is the classic “Red Light, Green Light” game where one person is a virtual stoplight and gives commands to the other players to either stop or go.
Rules of play
The player chosen as the current the stoplight says “Green Light!” and turns away from the other players. The other players move toward the stoplight player, from a distance set at the beginning of the game, and try to touch them. The stoplight player can at any time say “Red light!” and then turn around to face the other players. If the stop light player sees anyone still moving, they call them out and they are finished playing until a new game is started. The stoplight player repeats the red light, green light cycle. If one of the other players happens to touch the stop light player before they can turn around when saying “Red Light!”, then the current stoplight player moves to the beginning of the course and the other player becomes the stoplight. The game continues until only the the stoplight player remains.
In this remake of the game, we will use a micro:bit, its radio, and the accelerometer to enforce these rules!
Creating the stoplight
Let’s start with the code running on the stoplight’s micro:bit. Don’t use this code for the other players!
States
We define two states, or game conditions, called GREENLIGHT
and REDLIGHT
. A variable named state
will store the current game state. When the stoplight player presses A
, the game goes into “green light” mode. When they press B
, the state goes into “red light” mode.
let REDLIGHT = 0
let state = 0
let GREENLIGHT = 0
GREENLIGHT = 1
REDLIGHT = 2
Communication
The radio group for all game players is set to 1
. We will set the same group in the player’s code too. The game state is streamed in a ||basic:forever||
loop so that players continuously receive it.
let state = 0;
radio.setGroup(1)
basic.forever(function () {
radio.sendNumber(state)
})
Red light, green light
Use the ||radio:on button pressed||
block to run code when button A
and B
are pressed.
When A
is pressed, the game goes into GREENLIGHT
mode. When B
is pressed, the game
goes into REDLIGHT
mode. We also use ||basic:show icon||
to display the current game state.
let REDLIGHT = 0
let state = 0
let GREENLIGHT = 0
input.onButtonPressed(Button.A, function () {
state = GREENLIGHT
basic.showIcon(IconNames.Yes)
})
input.onButtonPressed(Button.B, function () {
state = REDLIGHT
basic.showIcon(IconNames.No)
})
GREENLIGHT = 1
REDLIGHT = 2
Stoplight code
All together the stoplight code looks like this:
let REDLIGHT = 0
let state = 0
let GREENLIGHT = 0
input.onButtonPressed(Button.A, function () {
state = GREENLIGHT
basic.showIcon(IconNames.Yes)
})
input.onButtonPressed(Button.B, function () {
state = REDLIGHT
basic.showIcon(IconNames.No)
})
GREENLIGHT = 1
REDLIGHT = 2
radio.setGroup(1)
basic.forever(function () {
radio.sendNumber(state)
})
Improve the game
- Use
||music:ring tone||
to play a sound while the game is inGREENLIGHT
mode. - Attach a servo and move the arm based on the game state.
The players
The code for the other players needs to listen for the stoplight’s state.
States
First, we again define the state constants GREENLIGHT
, REDLIGHT
, and set the radio group to 1
.
We also add a state
variable that will store the state of the game.
let REDLIGHT = 0
let state = 0
let GREENLIGHT = 0
GREENLIGHT = 1
REDLIGHT = 2
radio.setGroup(1)
Communication
We use the ||radio:on received number||
block to store the stoplight state into the state
variable.
let state = 0
radio.onReceivedNumber(function (receivedNumber) {
state = receivedNumber
})
Display
In a ||basic:forever||
loop, we display different icons based on the game state. Use a ||logic:if||
and
||basic:show icon||
blocks to display the game state.
let REDLIGHT = 0
let state = 0
let GREENLIGHT = 0
basic.forever(function () {
if (state == GREENLIGHT) {
basic.showIcon(IconNames.Yes)
} else if (state == REDLIGHT) {
basic.showIcon(IconNames.No)
}
})
Movement check
If the state
is equal to REDLIGHT
, we need to check that the player is not moving.
This is where the accelerometer comes into play. The accelerometer measures forces applied to the micro:bit.
If the player moves, it’s likely that the accelerometer will detect any small forces applied to the micro:bit.
At all times, gravity is applied to the micro:bit, so the acceleration strength at rest is always near 1000
mg.
If the acceleration strength is far from that value, say 1100
or 900
, we can assume that the player is moving. To compute this we use the formula:
moving = | acc strength - 1000 | > 100
Now that we know the math for it, we can turn this into code.
let REDLIGHT = 0
let state = 0
let GREENLIGHT = 0
let moving = false
if (state == REDLIGHT) {
moving = Math.abs(input.acceleration(Dimension.Strength) - 1000) > 100
if (moving) {
game.gameOver()
}
}
Player code
All together, the code for the players is:
let moving = false
let REDLIGHT = 0
let state = 0
let GREENLIGHT = 0
radio.onReceivedNumber(function (receivedNumber) {
state = receivedNumber
})
GREENLIGHT = 1
REDLIGHT = 2
radio.setGroup(1)
basic.forever(function () {
if (state == GREENLIGHT) {
basic.showIcon(IconNames.Yes)
} else if (state == REDLIGHT) {
basic.showIcon(IconNames.No)
}
if (state == REDLIGHT) {
moving = Math.abs(input.acceleration(Dimension.Strength) - 1000) > 100
if (state == REDLIGHT && moving) {
game.gameOver()
}
}
})
Tuning
Does the movement check work? Try changing the 100
value to tune the detection sensitivity. Try 64
maybe.
Improve the game
- Use
||music:ring tone||
to play a tone while in green mode. - Use the packet signal strength to detect that you’ve reached the stoplight.
radio